[Stoves] Powering a TLUD Fan

Phil Hughes nicafyl at gmail.com
Sat Sep 1 10:13:14 PDT 2012


I think this is a great suggestion. As much as I like electronic solutions
(because that is what I am good at) I can see some serious advantages here.
First, no batteries, electronics, ... is going to make it a lot easier to
keep systems operating. While electronics is generally reliable, it is
still going to be a lot easier to find a replacement innertube than a
replacement CMOS chip.

The only "critical part" is the control of the air flow. I expect there are
devices that do this just fine. Without doing any research, just a pressure
regulator like the kind you find on an air compressor should get you close.

The rest of the system is then subject to local adaptation. It could be a
flywheel-powered compressor in one place, a PV powered electric pump in
another (allowing you to store the air when the sun was shining and use it
whenever you want without the problem of batteries), water pressure, ...

On Sat, Sep 1, 2012 at 10:55 AM, <rongretlarson at comcast.net> wrote:

> Andrew and list:
>
>     This is to ask for your thoughts on a different approach to air
> control than a fan (with or without a battery).  That is to use a
> (pre-pumped) air storage "bladder".
>     My rationale for this query includes:
>     1.  energy storage via air (CAES) has quite a few proponents.  Large
> vehicles have operated on air storage (where electricity was a hazard) and
> there are companies building cars based on air storage..
>     2.  compressed air supply is common in many places - as air-motors are
> lighter weight and cheaper than electric.
>     3.  What is needed in TLUDs is controllable primary air - not
> electricity.  In Josh Kearn's bicycle-flywheel-fan proposal, one can
> compress air perhaps as easily as putting energy into a flywheel (using
> inner tubes or similar) and then conversion to a fan/blower.  That is - one
> is storing exactly what you want to supply - no energy conversions needed.
>     4.  I think there are controllable constant volume-flow valves - that
> would also allow controlling power levels (turn down ratios).
>     5.  Your use below of the term 1 cubic meter per 1 kg biomass sounds
> potentially doable with moderate size "bladders".  I have no idea how many
> atmospheres of pressure is reasonable, nor what material (if any) might be
> appropriate with simple TLUDs.  The issue only is whether air storage might
> be cheaper than other approaches.  As Crispin pointed out, the low pressure
> above the fuel supply reduces the needed pressure (but not the amount of
> needed air).
>     6.  The fact that the air will be heated going into the "bladder" and
> cooled coming out might not be a problem is the air is preheated by flowing
> downward through an outer air-tight "jacket" surrounding the fuel chamber.
>     7.  My gut feeling is that this will only work economically if a
> second use can be found for the "bladder".  Solar plus rechargeable
> batteries can be pretty cheap when you are also getting lighting, radio,
> cell-phone-recharging, etc.
>
> Ron
>
> ------------------------------
> *From: *ajheggie at gmail.com
> *To: *"Discussion of biomass cooking stoves" <
> stoves at lists.bioenergylists.org>
> *Sent: *Saturday, September 1, 2012 6:28:24 AM
> *Subject: *Re: [Stoves] Powering a TLUD Fan
>
>
> On Fri, 31 Aug 2012 04:54:18 +0700, Paul Olivier wrote:
>
> >The second is the pressure resistance of the fan (40x40x28mm).
> >For a gasifier of a 150 mm diameter, the pressure resistance has to be at
> >least 0.87 InAq.
>
> InAq being inches of water gauge above atmospheric? If so this is
> about 250 Pascal, so 1 kg of dry biomass burned per hour at
> stoichiometric air for complete gasification should be around 1m3 of
> air, the 5m3 of air needed for secondary combustion would not need to
> pass through the bed and as Crispin has said the offgas can entrain
> the secondary air, though this is work it probably isn't much compared
> with the resistance of the fuel bed. Rice husks have a high ash
> content so I'm guessing its the ash that is serving to increase
> resistance by blocking pores between the husks.
>
> Does the same happen with other fuels previously mentioned?
>
> 1m3 of cold air per hour is about 1/3 of a litre per second. As power
> is force time distance and pressure and volume have terms for distance
> that cancel out then power is pressure time volume per second in SI
> units.
>
> 250 Pascal times 0.0003 seems to be 0.075W so there seems to be a fair
> loss of conversion efficiency in the system somewhere, fans should be
> about 70% efficient but as things get small they tend to get more
> lossy. Or are my calculations wrong?
>
> Axial fans are particularly good at thrashing air into heat with no
> useful work as they stall, they are good at moving large volumes with
> little drop in pressure across them, laptop fans seem to be better as
> they tend to be centrifugal ones that push air along narrow ducts.
>
> AJH
>
>
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-- 
Phil Hughes
nicafyl at gmail.com
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